Initial commit with core utilities

Add core utilities for IP address handling, process information, and OS detection

- Introduce `guess_local_ip` function to determine local IP address
- Implement `list_all_ips` to list all non-loopback IP addresses
- Add `find_process_using_port` to identify processes using specific ports
- Include OS information utility with `get_os_string`
- Setup project structure with Cargo.toml, .gitignore, and documentation
- Add comprehensive tests for all utility functions
- Configure code style guidelines in AGENTS.md

AGENTS.md

@@ -0,0 +1,76 @@
+# pmoutils - Agent Guidelines
+
+## Build & Test Commands
+
+```bash
+# Build the library
+cargo build
+
+# Run all tests (unit + doctests)
+cargo test
+
+# Run a single unit test
+cargo test --lib ip_utils::tests::test_guess_local_ip
+
+# Run tests for a specific module
+cargo test --lib ip_utils::tests
+
+# Run only doctests
+cargo test --doc
+
+# Lint with clippy
+cargo clippy --all-targets -- -D warnings
+
+# Format code
+cargo fmt
+```
+
+## Code Style Guidelines
+
+### General
+- Rust 2024 edition
+- Follow official Rust style guide and Clippy recommendations
+- All code must be documented with Rustdoc comments
+- Prefer `&str` over `String` for function parameters when possible
+
+### Imports
+- Group imports by source: std → external crates → crate modules
+- Use `use` statements at the top of each module
+- Import specific items, not glob imports (`use std::net::IpAddr`, not `use std::net::*`)
+
+### Naming Conventions
+- Types: `PascalCase` (e.g., `ProcessPortInfo`, `TransportProtocol`)
+- Functions/methods: `snake_case` (e.g., `guess_local_ip`, `find_process_using_port`)
+- Constants: `SCREAMING_SNAKE_CASE`
+- Traits: prefix with `To` or descriptive noun (e.g., `ToXmlElement`)
+- Tests: `test_functionality_what_it_does` format
+
+### Error Handling
+- Use `Option` for operations that may not return a value (e.g., `find_process_using_port` returns `Option<ProcessPortInfo>`)
+- Use `?` operator for propagating errors
+- Return default values (like `"127.0.0.1"`) only when appropriate fallback exists
+- Document error conditions in function documentation
+
+### Types
+- Prefer concrete types over generics unless abstraction is needed
+- Use `u32` for PIDs, `u16` for ports
+- Use `String` for process names and owners (owned, mutable)
+- Derive `Debug` and `Clone` for data structures
+
+### Documentation
+- All public items require Rustdoc comments
+- Include `# Examples` section when useful
+- Document return values and error conditions
+- Use triple slashes `///` for module-level documentation
+
+### Formatting
+- Run `cargo fmt` before committing
+- Use 4 spaces for indentation (default Rust formatter)
+- Keep lines under 100 characters when possible
+
+### Testing
+- Unit tests in same file as code (in `mod tests {}` block)
+- Test names follow pattern: `test_<function>_<condition>`
+- Include tests for edge cases (e.g., fallback to localhost)
+- Verify return value formats and constraints
+- Test filtering: `cargo test --lib ip_utils::tests::test_list_all_ips_no_loopback`